The Pioneer M-22 is the original power amplifier from the Series 20 : old style Class A with no circuit trickery or audiophile touches - except where it really counts : power transformers, capacitors, resistors, chassis and ground paths.
The M-22 is a sound bolid.
"Open-guts" style with massive diecast heatsinks and chassis, four 33,000µF caps, full dual-mono layout.
If you don't mind having loudspeaker cables running in front of your rig... not very tidy.
But if you have an M-22 just for its sound qualities... all's fine : good-looking box that acts as room-heater on the side and ultimately makes wonderful music.
The dedicated japanese catalog is now at hand (2011) but nowhere near being translated...
A real M-22 here.